The present invention relates to interrogators, wireless communication systems, methods of operating an interrogator, methods of operating a wireless communication system and methods of determining range of a remote communication device.
Electronic identification systems typically comprise two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems are operable to provide such communications via a wireless medium.
One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, now U.S. Pat. No. 6,130,602, issued Oct. 10, 2000, assigned to the assignee of the present application, and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system including communication devices. The disclosed communication devices include an interrogator and a remote transponder, such as a tag or card.
Such communication systems can be used in various applications such as identification applications. The interrogator is configured to output a polling or interrogation signal which may comprise a radio frequency signal including a predefined code. The remote transponders of such a communication system are operable to transmit an identification signal responsive to receiving an appropriate polling or interrogation signal.
More specifically, the appropriate transponders are configured to recognize the predefined code. The transponders receiving the code can subsequently output a particular identification signal which is associated with the transmitting transponder. Following transmission of the polling signal, the interrogator is configured to receive the identification signals enabling detection of the presence of corresponding transponders.
Such communication systems are useable in identification applications such as inventory or other object monitoring. For example, a remote identification device is initially attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output an identification signal. Generating the identification signal identifies the presence or location of the identification device and the article or object attached thereto.
Some conventional electronic identification systems utilize backscatter communication techniques. More specifically, the interrogator outputs a polling signal followed by a continuous wave (CW) signal. The remote communication devices are configured to modulate the continuous wave signal in backscatter communication configurations. This modulation typically includes selective reflection of the continuous wave signal. The reflected continuous wave signal includes the reply message from the remote devices which is demodulated by the interrogator.
The present invention provides interrogators, wireless communication systems, methods of operating an interrogator, methods of operating a wireless communication system and methods of determining range of a remote communication device.
According to one aspect of the present invention, a wireless communication system including an interrogator and a plurality of remote communication devices is provided. The interrogator includes communication circuitry configured to output a plurality of wireless signals to the remote communication devices. Exemplary remote communication devices include radio frequency identification devices. The communication circuitry of the interrogator is further configured to receive plural wireless signals from the remote communication devices. In the described embodiment, the communication circuitry is configured to output a continuous wave signal and the remote communication devices are individually operable to backscatter modulate the continuous wave signal.
In certain aspects, a processor of the interrogator is configured to determine ranges of the remote communication devices relative to the interrogator. Such ranges may be calculated responsive to the received wireless signals. The processor of the interrogator can determine the phase of individual received wireless signals and can determine the range responsive to the phase determination. Communication circuitry of the interrogator can be configured to adjust the frequency of outputted wireless signals and to provide frequency adjustments of different magnitudes. In some aspects, the communication circuitry provides frequency adjustments of increasing magnitude over time.
Further, the processor of the interrogator of the described embodiment is configured to utilize a range determination from an initially received wireless signal to determine a range from a subsequently received wireless signal in some aspects.
Other structures and methods are provided according to other aspects of the present invention as described below.